1. Field of the Invention
The present invention relates to a liquid processing method and a liquid processing system, more specifically a liquid processing method and a liquid processing system for supplying a processing liquid, e.g., a chemical liquid to objects to be processed, e.g., semiconductor wafers, LCD glass substrates, etc.
2. Related Background Art
In fabrication processes for semiconductor devices and fabrication processes for LCDs, generally liquid processing methods (systems) using processing liquids, etc. are widely used so as to remove resists adhering to processed objects, such as semiconductor wafers, LCD glasses, etc., and residues (polymers, etc.) remaining after drying processing.
As a liquid processing method (system) of such conventional liquid processing methods (systems) is known a cleaning processing method in which processing liquids to be used in the cleaning processing are used in recycled liquids for the efficient use of the processing liquids of expensive chemical liquids.
The liquid processing system using such recycled liquid mainly comprises, as shown in FIG. 13, a heater 1 which is heating means for heating a processing liquid L stored in a tank 10 to a prescribed temperature; cooling means 2 which passes a cooling medium, e.g., cooling water, for cooling the processing liquid L when the processing liquid in the tank 10 exceeds a set temperature; a stand-by circulation line 5 having a stand-by circulation passage 4 which circulates the processing liquid L in the tank 10 outside the tank 10 for stand-by; a nozzle 7 which is processing liquid supply means for supplying the processing liquid to objects-to-be-processed, e.g., wafers W, in a processing chamber 6; a supply passage 8a which supplies the processing liquid to the nozzle 7; a wafer processing unit 9 having a discharge passage 8b; a first change-over valve V1 and a second change-over valve V2 as change-over means for communicating and discommunicating the stand-by circulation passage 4 of the stand-by circulation line 5 with the supply passage 8a and the discharge passage 8b of the processing unit 9; and a flow meter FM inserted in the cooling water passage 2a of the cooling means 2 on the side of the cooling water supply source 2A.
In such liquid processing system, detected signals are supplied to control means, e.g., a central processing unit 30 (hereinafter called a CPU 30) from a liquid temperature sensor S for detecting a temperature of the processing liquid L in the tank 10 and from a temperature sensor T for detecting a temperature of the heater 1, and the heater 1 is controlled (PID control: proportional operation, integral operation and differential operation control) to be at a prescribed temperature by a PID temperature controller R which is based on control signals from the CPU 30, so that the processing liquid L is set at an allowable processing temperature, e.g., in a monitor temperature range of, e.g., 70±1° C. A pump P is inserted in the stand-by circulation passage 4, and a filter F is inserted in the stand-by circulation passage 4 on the discharge side (a secondary side) of the pump P.
The liquid processing system having the above-described structure has two piping routes, i.e., the stand-by circulation line for the processing liquid L and the wafer processing circulation line. The first and the second change-over valves V1, V2 are controlled to change over each other to thereby change over the piping routes. However, in such conventional liquid processing system (method), because of different radiation amounts (temperature exchange rates) between the circulation line and the wafer processing circulation line, the PID control cannot follow the heater heating or the radiation of the system, and a state where a temperature of the processing liquid is away from a desired temperature takes place. That is, when the first change-over valve V1 and the second change-over valve are changed over with each other to communicate the stand-by circulation passage 4 with the supply passage 8a and with the discharge passage 8b, as shown in FIG. 14 the temperature of the processing liquid becomes lower by about 2° C. than the allowable temperature (monitor temperature range). This is because when the processing liquid of high temperature is fed into the processing chamber 6, and wafers W which are substantially the same as the atmospheric temperature (around 25° C.), the processing liquid is considerably deprived of the heat and returns into the tank. The processing liquid having deprived of the heat lowers the temperature of the processing liquid L in the tank 10. It takes about 2 minutes and 30 seconds for the lowered temperature to reach the allowable temperature. During this period of time, a problem that the processing becomes insufficient, e.g., a problem that the ability of removing polymers is lowered takes place. Resultantly, the processing efficiency and throughputs are lowered. When the processing has been completed, the first change-over valve V1 and the second change-over valve V2 are changed over with each other to communicate the supply passage 8a and the discharge passage 8b with the stand-by circulation passage 4, a phenomena that the temperature of the processing liquid is higher by about 2° C. than the allowable temperature thereof (monitor temperature range) takes place. This is because a processing state of the processing liquid where the processing liquid has a large radiation abruptly changes to the stand-by state where the processing liquid has a small radiation. It takes about 12 minutes for the processing liquid to reach the allowable temperature, and during this period of time, the next processing cannot be made, with a resultant problem of throughput decrease. The temperature rise of the processing liquid L exceeding the allowable processing temperature range causes the problems of not only deterioration of the processing liquid L but also decrease of the life of the processing liquid L.